Primer compositions are typically applied to substrates in order to provide a uniform color base to a substrate, for subsequent application of coatings to provide a desired visual effect. Substrates may have initial color variances due to the presence of stains or color differences in substrate materials, such as the color of unprimed drywall as compared to taped joints. Additionally, prior marking of the substrate, e.g. by pencil, pen, permanent marker and the like may provide particular priming challenges because the prior marks may be visually apparent when covered by an ineffective primer. Certain marks or stains may be particularly challenging, because the mark or stain may migrate from the substrate through the primer, so that the mark or stain is apparent on the surface of the primed substrate only after passage of some time. Migration of stains to the surface of coatings from the substrate is particularly a problem when the coatings are water-based, and the marking or stain comprises water-soluble materials. This is especially acute in the case of aqueous white coatings. Such staining is particularly a problem in coatings applied on woods such as red cedar or redwood, noted for its high water-soluble tannin content, or previously painted surfaces that have been marked with a water soluble marker.
Various treatments and coatings have been developed in an attempt to provide stain blocking characteristics. Typically, such coatings utilize the organic solvent nature of oil-based coatings. However, it is extremely desirable to find a water-based solution in the effort to reduce the emission of Volatile Organic Compounds (“VOCs”). To this end, a number of approaches for blocking of stains, and in particular tannin migration, using water-borne systems have been proposed.
There is a need in the art for a water-based approach for effective blocking of stains, and in particular tannin migration and water soluble marker stains, in a coating system having low VOC emissions.